1. Field of the Invention
The present invention relates to membrane seals, and in particular to membrane seals for sealing between high-pressure and low-pressure regions of a gas turbine engine or jet engine.
2. Description of the Related Art
The background art will be explained with reference to FIG. 1. Membrane seals are a common way of providing a fluid-tight seal between different pressure regions and are typically found in gas turbine engines and jet engines. Membrane seals of the type with which the present invention is concerned include a first radially inner annular sealing member 2 and a second radially outer annular sealing member 4 sealably connected together by an annular membrane 6. Both the first and second sealing members 2, 4 have a circular cross-section. In FIG. 1 the first and second sealing members 2, 4 are shown to have a solid cross-section but they can be tubular. The first sealing member 2 is contained within an annular sealing groove 8a formed by a radially inner track 10a having a U-shaped cross-section. Similarly, the second sealing member 4 is contained within an annular sealing groove 8b formed by a radially outer track 10b having a U-shaped cross-section. The two tracks 10a, 10b are mounted on a radially inner and radially outer portion of a gas turbine engine casing (not shown) respectively.
The membrane seal is positioned between a low-pressure region 12 of the engine and a high-pressure region 14 of the engine. The axial width of the sealing grooves 8a, 8b is slightly wider than the axial width of the first and second sealing members 2, 4. This means that the first and second sealing members 2, 4 can slide axially within the sealing grooves 8a, 8b. When the gas turbine engine is operating, the difference in pressure between the low-pressure region 12 of the engine and the high-pressure region 14 of the engine forces the membrane seal in the direction of the arrows. The first sealing member 2 is therefore forced into contact with a side face 16a of the track 10a to effect a fluid-tight seal. Similarly, the second sealing member 4 is forced into contact with a side face 16b of the track 10b to effect a fluid-tight seal.
A major disadvantage with conventional membrane seals is that the first and second sealing members suffer from premature wear and thermal attrition caused by the high levels of vibration encountered in the gas turbine engine.